I need an example of this please

A sturdy box or bench high enough that you can lie with your feet hanging down at 90 degrees. You will also need some way to anchor your feet on this; ring straps work very well

Which element and PE?

Lets say for GHR or Curl ups.   I am thinking ahead so I can prepare for it

I do arch ups off the arm of my coach. A piano stool or similar would also work.

I also did arch ups on the couch (could also use a sawhorse and hold feet in stall bars).  For GHR I used a bench (with a foam cushion) and held my feet with my stall bars.

Those are all awesome Ideas. I do not have stall bars though

That's a problem for me as well. I have a home made plyo box I can prop up on a couple of boards for extra height. Then I use straps anchored to something heavy to hold my feet. It's out in the garage though, not sure what I'll do over the winter.